Marine instruments such as depth finders, speed sensors, sonars and the like are mounted on boats, typically on the transom, so as to extend from the stern down into the water. Others are mounted forward of the boat's transom and project through the hull whereby the sensor portion of the sensor extends into the water forward of the transom.
In U.S. Pat. No. 4,898,029, there is disclosed a marine speed sensor of the paddle wheel type which projects through the hull of a boat with its paddle wheel outside the hull to be subjected to the flow of the water. The rotational speed of the paddle wheel is measured electronically to produce a visual readout indicating the boat's speed. The sensor mechanism, which, in this case, is the paddle wheel, projects from the hull and is connected by an electric cable to the readout dial which is frequently mounted on or near the instrument panel.
A generally flanged, tubular housing is permanently mounted in the hull of the boat and secured in place using a flanged nut. The sensor is inserted into the housing with its paddle wheel projecting outside of the hull and with the appropriate electric cable leading to the readout mechanism inside the hull. "O" rings on either or both of the housing or sensor, which is normally cylindrical, prevent the leakage of water into the boat when the sensor is in its operating position in its housing.
There are many times when it is desirable to remove the sensor from its housing as, for example, to remove growth such as barnacles from the surfaces exposed to sea water or to replace it with a blanking plug prior to haul-out, to prevent damage. Since the housing is permanently installed in the boat, in effect it is a hollow tube. When the sensor is removed, water will literally gush into the boat. For this purpose, a blanking plug having essentially the same configuration as the sensor is initially sold with the sensor to be inserted in the housing when the sensor is removed to stop the flow of water.
The technique of removing the sensor and replacing it with a blanking plug entails unscrewing a retaining nut, pulling the sensor from the housing, and pushing the blanking plug into place as quickly as possible. In this process, it is inevitable that water will enter the boat. With the housing located perhaps two to three feet below the waterline, a considerable "head" of water can cause a stream the diameter of the housing to rise a couple of feet into the boat even when an experienced, skillful person is removing the sensor and jamming the plug into place.
The present invention is directed toward remedying this situation.